Add gpu_main_thread_factory.h to expose less of content's guts.

content/browser/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//media/media_options.gni")
 import("//ppapi/features/features.gni")
 import("//printing/features/features.gni")
 import("//third_party/WebKit/public/public_features.gni")
@@ skipping 653 matching lines @@
     "gpu/compositor_util.cc",
     "gpu/compositor_util.h",
     "gpu/gpu_client.cc",
     "gpu/gpu_client.h",
     "gpu/gpu_data_manager_impl.cc",
     "gpu/gpu_data_manager_impl.h",
     "gpu/gpu_data_manager_impl_private.cc",
     "gpu/gpu_data_manager_impl_private.h",
     "gpu/gpu_internals_ui.cc",
     "gpu/gpu_internals_ui.h",
+    "gpu/gpu_main_thread_factory.cc",
+    "gpu/gpu_main_thread_factory.h",
     "gpu/gpu_process_host.cc",
     "gpu/gpu_process_host.h",
     "gpu/gpu_process_host_ui_shim.cc",
     "gpu/gpu_process_host_ui_shim.h",
     "gpu/shader_cache_factory.cc",
     "gpu/shader_cache_factory.h",
     "histogram_controller.cc",
     "histogram_controller.h",
     "histogram_internals_request_job.cc",
     "histogram_internals_request_job.h",
@@ skipping 1320 matching lines @@
   if (!is_component_build) {
     public_deps = [
       ":browser",
     ]
   } else {
     public_deps = [
       "//third_party/leveldatabase",
     ]
   }
 }